1. The Field of the Invention
The present invention relates to a coil having a plurality of turns.
2. Description of the Related Art
Modern electrical apparatuses often require many coils, which are mounted on the printed circuit boards of the relevant electrical apparatus. The coils should combine very good electrical properties with a compact construction and a great ease of mounting. From JP-A 06 036937, a coil having a magnetic core is known, in which the magnetic stray flux is minimized in that the turns of the coil and the core form a single part.
It is an object of the present invention to provide a coil having minimal stray losses through the air gap between the turns of the coil and which enables a simple and fully automatic mounting on a printed circuit board to be achieved.
With an air coil in accordance with the invention this object is achieved in that the turns include a magnetic material. According to the invention said object is achieved in that the turns include an outer layer for carrying an electric current and a magnetic material in their interior. Air gaps between individual turns of the coil produce a stray flux and adversely affect the electrical properties of such a coil. In order to avoid these air gaps, the turns of a coil in accordance with the invention consist of magnetic wire. The individual turns of the coil are firmly held together by the magnetic forces between these turns, as a result of which air gaps between the turns are avoided. For this purpose, the turns of the coils need neither be glued together nor need they be wound onto a core or held together by other additional means. The coil is wound to the desired shape and retains its shape as a result of the magnetic forces between the turns. This allows a simple manufacture, particularly in the case of production in large quantities.
One embodiment of the present invention is particularly suitable for uses in high frequency technology, which usually employs air coils without cores. In order to improve the conductivity for high frequency currents, the magnetic wire, from which the air coil is wound, is clad with a material which is particularly suitable for high frequency uses. For this purpose, the magnetic wire is clad with a layer of gold, silver or copper.
Another embodiment of the present invention substantially facilitates the mounting of the coil. To enable the automatic mounting machine to detect the shape of the coil and its correct mounting direction, the coil should provide the appropriate information to the automatic mounting machine. A simple possibility of providing this information is that the automatic mounting machine has a magnetic sensor, which detects the degree and the type of magnetization of the coil to be mounted. Since the magnetization differs in dependence on the length of the coil and differently magnetized wires can be used, different coils can be detected with the aid of their magnetic properties.
A further embodiment of the present invention enables the coil to be mounted fully automatically on printed circuit boards. Particularly, in the case of SMD mounting (Surface Mounted Device), this enables a high production rate to be obtained. During SMD mounting, the parts are secured to that side of the printed circuit board, on which they are mounted.